In the case of sealing a fluid at all times for controlling a flow passage within a container, for example, a shaft-sealing device using a sealing member has heretofore been utilized in general. As the sealing member in the shaft-sealing device, for example, an annular O-ring or packing substantially circular in cross section has been used for sealing a wide variety of fluids, such as air, water, oil and gas. Since the sealing member has a main function to seal a fluid, it is required to have high sealing performance.
For this reason, the sealing member is generally attached to a shaft that is a member on one side of a shaft-sealing device, or formed within a single plane in the radial direction of a hole and attached axially to a groove substantially rectangular in cross section, and has a crushing allowance compressed by the shape of the groove when fulfilling its function by the pressure of contact with a member on the other side of the shaft-sealing device. The O-ring, for example, is compressed by the crushing allowance to induce a repulsive force, and the sealability thereof with contact surface pressure by this repulsive force is achieved to attain shaft sealing.
In addition, since the sealing member is generally made of any of various synthetic rubber materials exhibiting appropriate compression stress within a range not inducing any excessive deformation, it is required to particularly have prescribed low-compression permanent distortion and further satisfy characteristics including antiweatherability, wear resistance, heat resistance, cold resistance, oil resistance and chemical resistance. Furthermore, since the sealing member is utilized for shaft-sealing devices in a wide variety of fields including the fields of automobiles, construction machines, aircraft, office automation equipment and industrial instruments, for example, materials are selected in accordance with the individual fields (intended purposes) to make the crushing allowance appropriate and, even in the case of being used in a kinetic state in which a shaft-sealing portion is moved or in a fixed state in which the shaft-sealing portion is not moved, it is required to have high durability, high insertability and a high pressing crack prevention property, not to mention the securement of a shaft-sealing function. Thus, since the first object of an ordinary shaft-sealing device is to heighten a sealing function with the sealing member, the position of the sealing member or fluid-sealing region is generally prescribed. For this reason, an apparatus having the sealing device built therein has a complicated internal configuration.
Assuming that an operation of switching the sealing region to an unsealing region is performed to move the sealing region and use the shaft-sealing device as various kinds of drive sources, it is necessary to provide a separate motion mechanism at a section to which the sealing member within the sealing region or housing is to be attached. As the motion mechanism, a screw-feeding mechanism, piston-cylinder mechanism, rotation mechanism can be raised and, in order to operate these mechanisms, it is also necessary to use some power means including human power, electricity, air, hydraulic pressure, a spring, etc.
On the other hand, a valve using a polymer actuator has been proposed in order to switch a sealing region to an open or closed state (refer to Patent Document 1, for example). The valve of Patent Document 1 uses an artificial muscle as a valving element and has a polymer actuator capable of switching a flow passage through deformation of the valving element per se without use of any complicated power means. The artificial muscle is made of electrostrictive elastic polymer film and deformed through an on-off operation of voltage to come into contact with or separate from a valve seat directly or via a sealing material, thereby opening or closing the flow passage. The valve of Patent Document 1 has an EPAM (Electroactive Polymer Artificial Muscle) structure in which the thin rubber-like polymer film (elastomer) is sandwiched between elastic electrodes and elongated in a planar direction (enlarged in diameter in a circumferential direction) through the application of voltage between the electrodes. In this artificial muscle, in order to make the amount of distortion or deformation larger, the electrodes are disposed over the entire voltage-applying region surface of the polymer film to increase the amount of electrical load to be injected